Flash smelting entails injecting a sulfidic material into a furnace space with the aid of a stream of oxidizing gas through appropriately designed burners, so that the injected feed "burns" while it is in a suspended state within the furnace chamber. One type of furnace that has been used for carrying out flash smelting on a commercial scale incorporates vertically disposed burners which inject the suspension of solids and gas vertically downwards into the shaft of the furnace. A second type of furnace employs burners which are inserted through a vertical wall of the furnace so as to inject the suspension in a generally horizontal direction. It is in association with the latter type of furnace that the burner of the present invention is particularly useful.
A detailed description of a furnace of the horizontal burner type, with which the present assignee has been associated for some time, can be found in the paper: "Oxygen Flash Smelting Swings Into Commercial Operation", Journal of Metals (1955) pp. 742-750. The furnace in question is one having a chamber in the shape of a rectangular room with an arched ceiling. Burners are provided in the shorter of the side walls, while the exhaust off-take is provided in the arched furnace roof. The furnace can be operated in a fully autogenous manner by using commercially pure (i.e., at least 95 percent) oxygen to inject the feed. Apart from obviating the need for additional fuel to maintain the smelting temperature, this method of operation offers the advantage of exhaust gases which are more concentrated in sulfur dioxide than would be the case if air were used instead of oxygen. As a result the flue gases are of lower volume and are more amenable to recovery of the sulfur dioxide therefrom.
It should be mentioned at this point that while the burner arrangement in the above described furnace is referred to for convenience as horizontal to distinguish it from the vertical burner arrangement, in practice it is preferred that the burner be tilted at a slight angle to the horizontal as described in co-pending Canadian application Ser. No. 281,906, of July 4, 1977, assigned in common with the present invention.
A burner which has been used in the horizontal burner apparatus described above can be descibed for simplicity as consisting of a generally cylindrical member which defines a mixing tunnel, and an assembly of co-axial pipes which abutt and communicate with one end of the mixing tunnel. The central pipe carries the particulate feed into the mixing tunnel, while the oxidant gas is discharged into the mixing tunnel through the annular space between the pipes. Because the mixing tunnel is disposed in an approximately horizontal direction, and because in general the particulate material to be smelted is fed under gravity from a point above the burner, the feed carrying pipe is not straight, but rather bent over at least a portion of its length. In using a burner of such design, the curvature of the feed pipe has been found to lead to problems. One of these is the tendency for the desired even flow of particles through the feed pipe to be adversely affected. A more serious problem is that abrasion of the wall of the mixing tunnel by the dry particulate solids tends to occur unless such solids are travelling in a direction which is substantially parallel to the axis of the mixing tunnel when they are discharged thereinto from the feed pipe. Such wear of the mixing tunnel wall can be quite extensive and places a severe limitation on the useful life of the burner.